The powder metallurgy art generally uses four standard temperature regimes for the compaction of a metal powder to form a metal component. These include chill-pressing (pressing below ambient temperatures), cold-pressing (pressing at ambient temperatures), hot-pressing (pressing at temperatures above those at which the metal powder is capable of retaining work-hardening), and warm-pressing (pressing at temperatures between cold-pressing and hot-pressing).
Distinct advantages arise by pressing at temperatures above ambient temperature. The tensile strength and work hardening rate of most metals is reduced with increasing temperatures, and improved density and strength can be attained at lower compaction pressures. The extremely elevated temperatures of hot-pressing, however, introduce processing problems and accelerate wear of the dies. Therefore, current efforts are being directed towards the development of warm-pressing processes and metal compositions suitable for such processes.
Warm-pressing also has the problem of wear of the die walls caused by ejecting the compacted part from the die. Various lubricants are currently employed, as in U.S. Pat. No. 4,955,798 to Musella et al., that allow pressing to be accomplished with lubricants having melting points up to 150.degree. C. (300.degree. F.). Pressing above this temperature with these known lubricants, however, results in degradation of the lubricant and leads to die scoring and wear.
Therefore, a need exists to formulate lubricated metal powder compositions capable of withstanding increased pressing temperatures. Such metal powder compositions would exhibit improved densities and other strength properties. Such powder compositions and pressing methods would enable among other benefits, increased densities at lower pressing pressures, lower ejection forces required to remove the compacted component, and reduced die wear.